1. Field of the Invention
The present invention relates to sandblasting apparatus and the like, and, more particularly, to an improved aspirator probe for use in supplying a suitable mixture of materials such as sand and air from a reservoir through a delivery hose to such devices as a sandblast control nozzle.
2. Prior Art
It is known to provide a portable sandblasting apparatus with a probe which can be inserted into a reservoir of sand for supplying a mixture of sand and air through a delivery hose to a control nozzle. The control nozzle is supplied with pressurized propulsion fluid such as compressed air and operates, as by aspiration, to draw a vacuum in the delivery hose and in the probe, whereby ambient air pressure moves sand through the probe and through the delivery hose to the nozzle. The nozzle introduces the sand into the flow of propulsion fluid and effects a forceful delivery of the sand in a controlled direction for treating workpiece surfaces.
One proposed probe construction includes two parallel tubes of unequal length positioned side-by-side and welded together. One of the tubes is longer than the other, and its upper end projects upwardly beyond the upper end of the other tube. The lower ends of both tubes are coextensive. The longer of the tubes is a delivery tube for supplying a mixture of sand and air through a delivery hose to a control nozzle. The shorter of the tubes is an air supply tube. Aligned holes are drilled through adjacent walls of the delivery and air supply tubes to provide a port which communicates both of the tubes. When the control nozzle is activated, pressurized propulsion fluid passing through the nozzle creates an aspiration effect which draws a vacuum in the delivery hose and in the delivery tube. Ambient air pressure operates on sand in the container to force sand into and through the delivery tube, and through the delivery hose to the control nozzle. As sand rises in the delivery tube, an additional aspiration effect operating in the probe causes air to be drawn into the delivery tube from the air supply tube through the communicating port. The air which is drawn into the delivery tube mixes with the sand to provide a sand and air mixture that is supplied to the control nozzle. The aspiration effect which operates within the probe provides a means of metering sand and air for supply to the control nozzle. Since aspiration takes place within the probe, the probe is known in the art as an aspirator probe.
One problem with the foregoing aspirator probe proposal is that the operation of the probe tends to change undesirably with variations in the pressure of the propulsion fluid which is supplied to the control nozzle. A further problem lies in a pulsating, relatively uneven delivery of sand which occasionally results with use of the probe. Another problem is that, in order to drill a communicating hole through abutting walls of the side-by-side delivery and air supply tubes, it is necessary to drill an additional hole through the opposite wall of one of the tubes in order to gain access to the area where a hole can be drilled through abutting walls of the two tubes. The drilling of this additional hole adds to fabrication cost. The presence of this additional hole is also found, in some instances, to detract from proper operation of the probe.